In the production of optical fibers, a resin coating is provided for protection and reinforcement immediately after spinning a molten glass fiber. A known structure of the resin coating consists of a primary coating layer of a flexible resin which is coated on the surface of optical fibers and a secondary coating layer of a rigid resin which is provided over the primary coating layer. A so-called optical fiber ribbon is known in the art in the application of optical fibers provided with a resin coating. The optical fiber ribbon is made from several elemental optical fibers, e.g. four or eight optical fibers, by arranging these fibers in a plane and fixing them with a binder to produce a ribbon structure with a rectangular cross section. The binder for preparing the optical fiber ribbon from several optical fibers is called a ribbon matrix material. A multiple core ribbon structure consisting of several optical fiber ribbons is also known. The material for binding the optical fiber ribbons is called a bundling material.
An up-jacketing fiber with a thick coating layer provided over colored optical fiber is also known. The resin composition for producing such a thick coating layer is called an up-jacketing material.
The characteristics required for curable resins used as the coating materials for optical fibers include: a liquid at room temperature with a sufficiently low viscosity to be excellently coated; superior shelf life maintaining even composition distribution; good productivity at a high curing rate; sufficient strength and superior flexibility; very little physical change during temperature change over a wide range; superior heat resistance and superior resistance to hydrolysis; superior long term reliability with little physical change over time; superior resistance to chemicals such as acids and alkalis; low moisture and water absorption; superior light resistance; high resistance to oils; little hydrogen gas generation which adversely affects optical fiber characteristics; production of cured products with slippery surfaces.
In addition, in the manufacture of optical fiber ribbons and multiple core optical fiber ribbons it is important that the ribbons manufactured be smoothly wound and the wound ribbons be smoothly drawn out at a specific rate to smoothly manufacture optical fiber cables in the succeeding step. Conventionally, a lubricant such as silicone oil or a powder such as talc has been applied to the surface of the ribbon to provide a slippery surface, whereby smooth wind-up and draw-out operations of the optical fiber ribbons are ensured.
Another method to provide good surface slip characteristics is a method of including an additive such as silicone oil in the ribbon matrix material or the bundling material. The use of conventional additives, however, impairs the shelf life of the composition, that is, the addition of a large amount of additive causes the liquid composition to separate into two layers during storage, although the surface slip characteristics of the cured product are improved. If the amount of such an additive is too small, it is necessary to apply a powder such as talc when ribbons are produced, because the cured product does not have sufficient surface slip characteristics, even though the shelf life is excellent.
Furthermore, in a curable resin used as an up-jacketing material, a cured coating material must be easily removed in the course of fiber splicing.
The addition of silicone oil to up-jacketing materials has been known to allow the coated resin to be removed with ease. The use of conventional additives, however, impairs the shelf life of the composition, that is, the addition of a large amount of additive causes the liquid composition to separate into two layers during storage, although the cured material can be easily removed. If the amount is too small, no sufficient characteristics of cured product removal can be obtained, even though the shelf life is excellent.